Muscles stockpile power for future use

Muscles can “remember” the exercise from your youth, scientists have discovered, turning a popular theory on its head...

For anyone who hits the gym, you’ll know that lifting weights increases muscle mass and a lack of movement results in the muscles shrinking. As the largest cells in the body, muscle cells contain multiple control centres called nuclei. But what happens to these important command centres when the muscles waste away?

To try and explain this, there is a theory called the “myonuclear domain hypothesis” which states that as muscles grow, extra nuclei are added to help support the bigger cell. It is then believed that they are lost if the muscle shrinks. The growth side of this theory is widely accepted by scientists, however, the fate of nuclei when muscle is wasting is hotly disputed. Professor Larry Schwartz from the University of Massachusetts at Amherst, recently published in Frontiers in Physiology, weighed in on the debate. When asked about the theory he says “for a lot of reasons that was counterintuitive for what some of us in field knew about how cells destroy their nuclei, so we wanted to test that hypothesis.”

To do just that, the tobacco hawkmoth, a type of insect which has defined muscle growth and wastage during its lifespan, was studied to determine what happens to muscle nuclei number over time. Once they had isolated the muscle cells, they used a special dye to stain the cells allowing each nucleus to be counted. They also extracted all the DNA (the nucleus filling) and analysed this, resulting in two independent measures of nuclei content. “What we found was even though the muscles went through this dramatic loss of mass...they never lost their nuclei and didn’t lose their DNA” Schwartz explains.

This certainly turns the hypothesis on its head, Schwartz has experimental evidence that once a muscle cell gains a nucleus it gets to keep it. He goes on to explain how this finding impacts the general public, “when you are young and can exercise easily, you have a good pool of stem cells that can help your muscle grow and acquire extra nuclei.” This means that even if you lose muscle mass, when you go back to exercise you can build up your muscles much more quickly. “This is a phenomenon known as muscle memory. If you have banked these nuclei when you’re young you can draw on them again when you’re much older.” says Schwartz. This highlights how important it is to exercise while young and able, as it’s an investment for your health later in life.

But what about athletes who abuse biology and use steroids to enhance their muscles and performance? “It’s a little bit sneaky on their part, because they can use the steroids to build up their muscles and acquire those extra nuclei. Then when they go off the steroids, after a period of time it can no longer be detected, so they’ll pass the test” explains Schwartz, “people that have cheated with steroids get that benefit for the rest of their professional athletic life. They can never undo the benefit they’ve acquired.” So even with a public apology, a cheating athlete will always have a biological edge over competitors.